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<a name="Macro"></a>
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<hr>
<a name="g_t_002emacro"></a>
<h3 class="section">7.58 <code>.macro</code></h3>

<a name="index-macros"></a>
<p>The commands <code>.macro</code> and <code>.endm</code> allow you to define macros that
generate assembly output.  For example, this definition specifies a macro
<code>sum</code> that puts a sequence of numbers into memory:
</p>
<div class="example">
<pre class="example">        .macro  sum from=0, to=5
        .long   \from
        .if     \to-\from
        sum     &quot;(\from+1)&quot;,\to
        .endif
        .endm
</pre></div>

<p>With that definition, &lsquo;<samp>SUM 0,5</samp>&rsquo; is equivalent to this assembly input:
</p>
<div class="example">
<pre class="example">        .long   0
        .long   1
        .long   2
        .long   3
        .long   4
        .long   5
</pre></div>

<dl compact="compact">
<dt><code>.macro <var>macname</var></code>
<a name="index-_002emacro-macname"></a>
</dt>
<dt><code>.macro <var>macname</var> <var>macargs</var> &hellip;</code>
<a name="index-_002emacro-macname-macargs-_2026"></a>
</dt>
<dd><a name="index-macro-directive"></a>
<p>Begin the definition of a macro called <var>macname</var>.  If your macro
definition requires arguments, specify their names after the macro name,
separated by commas or spaces.  You can qualify the macro argument to
indicate whether all invocations must specify a non-blank value (through
&lsquo;<samp>:<code>req</code></samp>&rsquo;), or whether it takes all of the remaining arguments
(through &lsquo;<samp>:<code>vararg</code></samp>&rsquo;).  You can supply a default value for any
macro argument by following the name with &lsquo;<samp>=<var>deflt</var></samp>&rsquo;.  You
cannot define two macros with the same <var>macname</var> unless it has been
subject to the <code>.purgem</code> directive (see <a href="Purgem.html#Purgem">Purgem</a>) between the two
definitions.  For example, these are all valid <code>.macro</code> statements:
</p>
<dl compact="compact">
<dt><code>.macro comm</code></dt>
<dd><p>Begin the definition of a macro called <code>comm</code>, which takes no
arguments.
</p>
</dd>
<dt><code>.macro plus1 p, p1</code></dt>
<dt><code>.macro plus1 p p1</code></dt>
<dd><p>Either statement begins the definition of a macro called <code>plus1</code>,
which takes two arguments; within the macro definition, write
&lsquo;<samp>\p</samp>&rsquo; or &lsquo;<samp>\p1</samp>&rsquo; to evaluate the arguments.
</p>
</dd>
<dt><code>.macro reserve_str p1=0 p2</code></dt>
<dd><p>Begin the definition of a macro called <code>reserve_str</code>, with two
arguments.  The first argument has a default value, but not the second.
After the definition is complete, you can call the macro either as
&lsquo;<samp>reserve_str <var>a</var>,<var>b</var></samp>&rsquo; (with &lsquo;<samp>\p1</samp>&rsquo; evaluating to
<var>a</var> and &lsquo;<samp>\p2</samp>&rsquo; evaluating to <var>b</var>), or as &lsquo;<samp>reserve_str
,<var>b</var></samp>&rsquo; (with &lsquo;<samp>\p1</samp>&rsquo; evaluating as the default, in this case
&lsquo;<samp>0</samp>&rsquo;, and &lsquo;<samp>\p2</samp>&rsquo; evaluating to <var>b</var>).
</p>
</dd>
<dt><code>.macro m p1:req, p2=0, p3:vararg</code></dt>
<dd><p>Begin the definition of a macro called <code>m</code>, with at least three
arguments.  The first argument must always have a value specified, but
not the second, which instead has a default value. The third formal
will get assigned all remaining arguments specified at invocation time.
</p>
<p>When you call a macro, you can specify the argument values either by
position, or by keyword.  For example, &lsquo;<samp>sum 9,17</samp>&rsquo; is equivalent to
&lsquo;<samp>sum to=17, from=9</samp>&rsquo;.
</p>
</dd>
</dl>

<p>Note that since each of the <var>macargs</var> can be an identifier exactly
as any other one permitted by the target architecture, there may be
occasional problems if the target hand-crafts special meanings to certain
characters when they occur in a special position.  For example, if the colon
(<code>:</code>) is generally permitted to be part of a symbol name, but the
architecture specific code special-cases it when occurring as the final
character of a symbol (to denote a label), then the macro parameter
replacement code will have no way of knowing that and consider the whole
construct (including the colon) an identifier, and check only this
identifier for being the subject to parameter substitution.  So for example
this macro definition:
</p>
<div class="example">
<pre class="example">	.macro label l
\l:
	.endm
</pre></div>

<p>might not work as expected.  Invoking &lsquo;<samp>label foo</samp>&rsquo; might not create a label
called &lsquo;<samp>foo</samp>&rsquo; but instead just insert the text &lsquo;<samp>\l:</samp>&rsquo; into the
assembler source, probably generating an error about an unrecognised
identifier.
</p>
<p>Similarly problems might occur with the period character (&lsquo;<samp>.</samp>&rsquo;)
which is often allowed inside opcode names (and hence identifier names).  So
for example constructing a macro to build an opcode from a base name and a
length specifier like this:
</p>
<div class="example">
<pre class="example">	.macro opcode base length
        \base.\length
	.endm
</pre></div>

<p>and invoking it as &lsquo;<samp>opcode store l</samp>&rsquo; will not create a &lsquo;<samp>store.l</samp>&rsquo;
instruction but instead generate some kind of error as the assembler tries to
interpret the text &lsquo;<samp>\base.\length</samp>&rsquo;.
</p>
<p>There are several possible ways around this problem:
</p>
<dl compact="compact">
<dt><code>Insert white space</code></dt>
<dd><p>If it is possible to use white space characters then this is the simplest
solution.  eg:
</p>
<div class="example">
<pre class="example">	.macro label l
\l :
	.endm
</pre></div>

</dd>
<dt><code>Use &lsquo;<samp>\()</samp>&rsquo;</code></dt>
<dd><p>The string &lsquo;<samp>\()</samp>&rsquo; can be used to separate the end of a macro argument from
the following text.  eg:
</p>
<div class="example">
<pre class="example">	.macro opcode base length
        \base\().\length
	.endm
</pre></div>

</dd>
<dt><code>Use the alternate macro syntax mode</code></dt>
<dd><p>In the alternative macro syntax mode the ampersand character (&lsquo;<samp>&amp;</samp>&rsquo;) can be
used as a separator.  eg:
</p>
<div class="example">
<pre class="example">	.altmacro
	.macro label l
l&amp;:
	.endm
</pre></div>
</dd>
</dl>

<p>Note: this problem of correctly identifying string parameters to pseudo ops
also applies to the identifiers used in <code>.irp</code> (see <a href="Irp.html#Irp">Irp</a>)
and <code>.irpc</code> (see <a href="Irpc.html#Irpc">Irpc</a>) as well.
</p>
</dd>
<dt><code>.endm</code>
<a name="index-_002eendm"></a>
</dt>
<dd><a name="index-endm-directive"></a>
<p>Mark the end of a macro definition.
</p>
</dd>
<dt><code>.exitm</code>
<a name="index-_002eexitm"></a>
</dt>
<dd><a name="index-exitm-directive"></a>
<p>Exit early from the current macro definition.
</p>
<a name="index-number-of-macros-executed"></a>
<a name="index-macros_002c-count-executed"></a>
</dd>
<dt><code>\@</code>
<a name="index-_005c_0040"></a>
</dt>
<dd><p><code>as</code> maintains a counter of how many macros it has
executed in this pseudo-variable; you can copy that number to your
output with &lsquo;<samp>\@</samp>&rsquo;, but <em>only within a macro definition</em>.
</p>
</dd>
<dt><code>LOCAL <var>name</var> [ , &hellip; ]</code>
<a name="index-LOCAL-name-_005b-_002c-_2026-_005d-1"></a>
</dt>
<dd><p><em>Warning: <code>LOCAL</code> is only available if you select &ldquo;alternate
macro syntax&rdquo; with &lsquo;<samp>--alternate</samp>&rsquo; or <code>.altmacro</code>.</em>
See <a href="Altmacro.html#Altmacro"><code>.altmacro</code></a>.
</p></dd>
</dl>

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